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. 2021 Aug 4;16(1):29.
doi: 10.1186/s12995-021-00321-3.

Association between household exposure and cycle threshold in COVID-19 infected health care workers

Ai Chien  1   2 , Sandra Domeracki  1   3 , Sandeep Guntur  1   2 , Kristopher Taylor  1 , Chuanyi M Lu  1   4 , Harry Lampiris  1   5 , Paul D Blanc  6   7
Affiliations

Association between household exposure and cycle threshold in COVID-19 infected health care workers

Ai Chien et al. J Occup Med Toxicol. .

Abstract

Objective: Household SARS-COV-2 contact constitutes a high-risk exposure for health care workers (HCWs). Cycle threshold (Ct) of reverse transcriptase-polymerase chain reaction testing provides an estimate of COVID-19 viral load, which can inform clinical and workplace management. We assessed whether Ct values differed between HCWs with COVID-19 with and without household exposure.

Methods: We analyzed HCW COVID-19 cases whose Ct data could be compared. We defined low Ct at a cut-point approximating a viral load of 4.6 × 106 copies per ml. Logistic regression tested the association of household exposure and symptoms at diagnosis with a low Ct value.

Results: Of 77 HCWs with COVID-19, 20 were household exposures cases and 34 were symptomatic at testing (7 were both household-exposed and symptomatic at testing). Among household exposures, 9 of 20 (45%) manifested lower Ct values compared to 14 of 57 (25%) for all others. In a bivariate model, household exposure was not statistically associated with lower Ct (Odds Ratio [OR] 1.20; 95% Confidence Interval [CI] 0.97-1.51). In multivariable modelling both household exposure (OR] 1.3; 95% CI 1.03-1.6) and symptoms at diagnosis (OR 1.4; 95% CI 1.15-1.7) were associated with a low Ct value.

Discussion: Household exposure in HCWs with newly diagnosed COVID-19 was associated with lower Ct values, consistent with a higher viral load, supporting the hypothesis that contracting COVID-19 in that manner leads to a greater viral inoculum.

Keywords: COVID-19; Cycle threshold; Health care workers; Household exposure.

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Conflict of interest statement

The authors declare that they have no competing interests.

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